i#3848: Fix rseq assert from seccomp (#3879)
i#3848: Fix rseq assert from seccomp (#3879)

Adds allowance for seccomp blocking SYS_rseq.
Tested in a default docker run:
$ docker run <image> bin64/drrun -debug -- ls

Fixes #3848
AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio